This invention relates to spectroanalytical systems, and more particularly to spectroanalytical systems of the type that employ absorption phenomena.
It is frequently desirable to accurately determine several different elemental constituents of a sample in a single sample run of short duration.
In accordance with one aspect of the invention, there is provided a spectroanalytical system with a plurality of radiation sources and structure defining an analysis region that includes means for thermally energizing a sample material to be analyzed. Analysis beam path defining structure includes means for passing a radiation beam from a radiation source along the analysis beam path through the analysis region for modification by sample material in the analysis region. Analysis structure includes radiation dispersing structure arranged to disperse radiation in the analysis beam path with a spectrum and a radiation sensor. First transducer structure moves the dispersing structure relative to the beam path to apply a selected portion of the radiation dispersed by the dispersing structure to the radiation sensor. Source selector structure is disposed in the analysis beam path for selecting radiation from one of the radiation sources along the analysis beam path, second transducer structure is coupled to the source selector structure for directing radiation from a particular radiation source along the analysis beam path, and control structure coordinately operates the two transducer structures to apply a particular dispersed wavelength of radiation from the selected radiation source to the radiation sensor.
In a preferred embodiment, the optical system includes a bank of cassettes containing up to eight hollow cathode lamps, a galvanometer driven mirror for lamp selection, a high-resolution monochromator with a galvanometer driven grating for line selection that can traverse its entire wavelength range of greater than five hundred nanometers in less than one hundred (e.g., twenty milliseconds, a dual beam optical pathway, and a high sensitivity photomultiplier detector. Wavelength calibration is accomplished via a mercury reference lamp which is monitored via a retractable mirror.
The grating galvanometer is synchronized with the hollow cathode lamp selection mirror control galvanometer, and the accuracy of both galvanometer drives is continuously and automatically verified by the controller throughout the analytical process. Optional double beam optics utilize a second retractable mirror which is automatically moved into the analytical beam by the controller prior to the sample measurement to execute a reference beam measurement and then automatically retracted to measure the sample beam with optimal light efficiency.
The system can be configured with a single lamp mount, one four-lamp cassette or two four-lamp cassettes. Up to eight elements can be measured in an unattended run using similar single element lamps, and more than sixteen elements can be measured when multi-element (dual-element) lamps are used. The choice of elements to determine concurrently by flame atomic absorption analysis is based on the recommended flame oxidant, either air or nitrous oxide. The choice of an element pair for furnace atomic absorption is a function of the temperature necessary to volatilize the element from the graphite surface. The system can incorporate various sample input systems, including, for example the monitoring of the effluent from a chromatographic column.
Other features and advantages of the invention will be seen as the following description of a particular embodiment progresses, in conjunction with the drawings, in which:
FIG. 1 is a diagram of a spectroanalytical system in accordance with the invention;
FIG. 2 is a perspective view of a source selector mirror assembly employed in the system shown in FIG. 1;
FIG. 3 is a top view of a source assembly employed in the system of FIG. 1;
FIG. 4 is a front elevational view of the source assembly shown in FIG. 3;
FIG. 5 is a side elevational view of the source assembly shown in FIG. 3;
FIG. 6 is a bottom plan view of the source assembly shown in FIGS. 3-5 showing aspects of the drive system;
FIG. 7 is a diagram of circuitry employed in the drive system shown in FIGS. 6; and
FIG. 8 is a graph of a multi-element measurement made with the system shown in FIG. 1.